Gel patches are a type of poultice produced by coating a plaster containing a drug onto a support such as a fabric, and they generally include a large amount of water, have a thick plaster, and have low skin irritation. However, the adhesive force is usually reduced with the passage of time after the gel patch has been applied, and therefore ways of minimizing reduction in adhesive force have been studied, as described in PTLs 1 and 2, for example.